Photographic developer antioxidant



United States Patent Gfiice 2,902,367 Patented Sept. .1, 1959 PHOTOGRAPHIC DEVELOPER ANTIOXIDAN T Laurence G. Welliver, Binghamton, and Jerry S. Krizka,

Johnson City, N.Y., assignors to General Aniline &

Film Corporation, New York, N.Y., a corporation of Delaware No Drawing. Application December 26, 1957 Serial No. 705,145 5 Claims. (Cl. 9666) This invention relates to an improvement in photographic developer solutions, particularly those used in the graphic arts which are characterized by a low sulfite content.

Processing of graphic arts films to their desired high contrast which may exceed a gamma of involves the use of special developers. These developers have a very low sulfite content and use hydroquinone as the sole developing agent. They largely depend for their operation on the oxidation products formed by the hydroquinone. Because of the instability of this developing agent at the high pH at which it is used, it oxidizes quite rapidly, especially since the sulfite content is extremely low.

Sodium sulfite, which is the antioxidant and stabilizing agent commonly used in developing solutions, must be omitted entirely or used only in very small amounts in the graphic arts types of developers, since a quantity sufficient to prevent oxidation would impair the gradation or destroy the proper developing action of the developer.

It is, therefore, an obiect of this invention to provide graphic arts developers which are stable to aerial oxidation in spite of their low sulfite content. Other objects will be apparent from the following description.

We have found that the stability of photographic de velopers which contain hydroquinone as the sole developing agent and which are substantially free of sulfite ions can be improved by adding to such developers a stabilizing amount of boron acid including boron anhydride, boric acid, the polyboric acids and the water soluble salts of such boron acids as illustrated by orthoboric acid, metaboric acid, boric anhydride, sodium metaborate or sodium tetraborate, particularly borax. We have found that the optimum concentration of the boron compound expressed in terms of boric acid lies in the range of from 5 to 25 grams per liter, an amount of from 10 to 20 grams per liter being preferred. Instead of boric acid, the equivalent weights (molar equivalents) of alkali metal salts of boric acid such as borax or sodium metaborate are equally effective.

The oxidation inhibiting action of borate ions is very selective; it is limited to developers which contain hydroquinone as the sole developing agent and ineffective with the other hydroxybenzene developing agents such as pyrogallol and catechol. It is also ineifective in the presence of other conventional agents such as metol and phenidone which are often used in combination with hydroquinone. The stabilizing action of boron compounds likewise drops off sharply as the concentration of sodium sulfite is increased while the stabilizing action is still efi icient at a concentration of 5.0 grams of sodium sulfite per liter; it is virtually nonexistent when the sodium sulfite concentration exceeds 10.0 grams per liter.

We are aware that various boron acids and their alkali metal salts have been used previously in photographic developers. Boron acids and their anhydrides have been proposed as stabilizers for dry developer powders while the alkali metal salts, particularly sodium metaborate, have been proposed as the principal alkaline components in developer formulations. In all instances in which the use of boron acids and their alkali metal salts had been proposed, and this includes lithographic developers which are now obsolete, the alkali metal sulfite concentration was so high that protection against aerial oxidation was already provided by the sulfite and the boron acid was without eifect. The boric acid, as well as its salts, was merely used for pH control.

The developers which are contemplated herein contain as their essential components hydroquinone as sole developing agent, an alkali such as sodium carbonate either alone or together with sodium hydroxide and an antifogging agent taken from the group of alkali metal bromides. They contain also a very small amount of sulfite, not exceeding 5.0 grams per liter, either through direct additions or furnished through the partial dissociation of formaldehyde-bisulfite which is used in lithographic developers. The amount of suliite present in lithographic developers prepared from formaldehyde-bisulfite is determined by a quantitative analysis and expressed in terms of anhydrous sulfite and was found not to exceed 1.5 grams per liter.

Developers with these components which we have found to be stable against aerial oxidation when exposed to air in liquid form may be compounded in the following proportions:

LITHOGRAPHIC DEVELOPERS WITH FORMALDEHYDE BISULFITE Grams Hydroquinone 6 to 25 Formaldehyde bisulfite 20 to 60 Alkali metal carbonate (sodium carbonate monohydrate) 20 to Boron acid 5 to 25 Alkali metal bromide 0.5 to 5 Water to make 1.0 liter.

LITHOGRAPHIC DEVELOPERS WITHOUT FORMALDEHYDE BISULFITE Water to make 1.0 liter.

This developer was stored in an open tray and after four hours showed no significant changes in photographic characteristics due to aerial oxidation. When a type developer prepared without boric acid but otherwise identical and having the same photographic properties was stored under the same conditions and for the same length of time, the solution turned dark brown and its photographic activity was virtually destroyed.

Example II Grams Hydroquinone 22.5 Sodium sulfite 5.0 Sodium carbonate, monohydrate 55.0 Sodium metaborate 20.0 Potassium bromide 3.0

Water to make 1.0 liter.

When this developer was stored in open trays for six hours, the solution turned light straw color but showed no noticeable loss in photographic activity. The same developer without sodium metaborate, but adjusted to be otherwise photographically equal when fresh, discolored to a. dark brown color during storage and showed a pronounced loss in photographic activity exceeding one stop in effective speed.

Example III Grams Hydroquinone 22.5 Sodium su-lfite 5.0 Sodium carbonate, monohydrate 75.0 Borax- 15.0 Potassium bromide 3.0 Water to make 1.0 liter.

This developer was stored for eight hours in an open tray without noticeable discoloration or change in protographic properties. A comparison developer in which the borax'had been replaced byv an additional amount of sodium carbonate sufficient to provide the same pH and the same photographic properties discolored rapidly and became unuseable after four hours.

Example IV Grams Hydroquinone. 15.0 Formaldehyde bisulfite 50.0 Sodium. carbonate 20.0 Sodium metaborate 20.0 Potassium bromide 1.5 Water to. make 1.0 liter.

This developer can be used in an open tray for an entire working day of eight hours without deterioration due to aerial oxidation. When the metaborate was omitted from. the formula, the solution turned dark brown and it's photographic activity was virtually destroyed after four hours.

Example V Grams Hydroquinone 15.0 Formaldehyde bisulfite 40.0 Sodium: carbonate, monohydrate 70.0 Sodium bromide 1.0 Boric anhydride 8.0 Water to make 1.0 liter.

This. developer could be used in an open tray for an entire working day. A type developer which did not contain the boric anhydride became completely discolored and photographically useless after four hours.

Example VI Grams Hydroquinone 15,0 Formaldehyde bisulfite 45.0 Sodium. carbonate, monohydrate 55.0 Borax. 17 Sodium bromide 1,1 Water to make 1.0 liter.

This developer was used in an open tray for eight hours Grams Hydroquinone 12.0 Sodium sulfite 2.0 Sodium carbonate, monohydrate 36.0 Boric acid 18.0 Sodium hydroxide 12.0 Potassium bromide 1.0

2. A photographic developer solution stabilized against aerial oxidation containing as its essential ingredientsfor one liter of developer solution:

Grams Hydroquinone 15.0 Formaldehyde bisulfite 50.0 Sodium carbonate 20.0 Sodium metaborate 20.0 Potassium bromide 1.5

3. A photographic developer solution stabilized against aerial oxidation containing as its essential ingredients'for one liter of developer solution:

Grams Hydroquinone 15.0 Formaldehyde bisulfite 40.0 Sodium carbonate, monohydrate 70.0 Sodium bromide 1.0 Boric anhydride 8.0

4. A photographic developer solution stabilized against aerial oxidation containing as its essentialingredients for one liter of developer solution:

Grams Hydroquinone 22.5 Sodium sulfite 5.0 Sodium carbonate, monohydrate 55.0- Sodium metaborate 20.0- Potassium bromide 3.0

5. A photographic developer solution stabilized against aerial oxidation containing as its essential ingredients for one liter of developer solution:

Grams Hydroquinone 15.0 Formaldehyde bisulfite 45.0 Sodium carbonate, monohydrate 55.0 Borax 17.0 Sodium bromide 1.1

References Cited in the file of this patent UNITED STATES PATENTS 2,313,523 Donovan et a1. Mar. 9, 1943 FOREIGN PATENTS 643,411 Great Britain Sept. 20, 1950 OTHER REFERENCES Photo-Lab-Index, pages 5-19, copyright 1957. in Div. 60.) 

1. A PHOTOGRAPHIC DEVELOPER SOLUTION STABILIZED AGAINST AERIAL OXIDATION CONTAINING AS ITS ESSENTIAL INGREDIENTS FOR ONE LITER OF DEVELOPER SOLUTION: 